Berlin 2008 – scientific programme
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O: Fachverband Oberflächenphysik
O 74: Metal Substrates: Adsorption of O and/or H
O 74.9: Talk
Thursday, February 28, 2008, 17:00–17:15, MA 141
Femtosecond laser desorption of atomic hydrogen from graphite in the visible and in the XUV using FLASH — •Robert Frigge1, Tim Hoger1, Björn Siemer1, Carsten Thewes1, Marcus Rutkowski1, Helmut Zacharias1, Stefan Düsterer2, and Rolf Treusch2 — 1Physikalisches Institut, Münster, Germany — 2Hasylab, Hamburg, Germany
The desoption of hydrogen from HOPG is of great interest in astrophysics. In so called H-I-clouds particles form areas of higher density in which protostars develop. The rise of protostars out of H clouds is not yet fully understood. This talk presents the laser desorption of hydrogen from HOPG. The velocity distribution of atomic hydrogen from HOPG is examined after surface excitation with fs pulses of 800 nm and 400 nm from a Ti:Sa laser system and 32 nm from a free electron laser(FLASH).
The atomic hydrogen is ionised via the 1s → 2s transition using a 2+1 REMPI detection scheme. Ionised H atoms are detected by a time-of-flight mass spectrometer. The arrival time distribution of H atoms at the ionised volume is measured by varying the delay between the pump and the probe laser. The transformation into a velocity distribution yields extremely slow velocities. The results are discussed more generally with the two temperature model and also in light of a recent DFT calculation.
[Hornekaer et al., Phys. Rew. Lett.97, 186102 (2006)]